What is a PET scan?

Professor Joanna Wardlaw talks to Senior Cardiac Nurse Emily McGrath about the scans that show signs of dementia, blocked arteries and other problems.

 PET scans of the brain

PET scans of the brain

1. Why would I have a PET scan?

PET (short for positron emission tomography) scans are good at showing how the tissues of your body are actually working.

There are two types: PET combined with a CT (computerised tomography) scan and PET combined with an MRI (magnetic resonance imaging) scan. The commonest type is PET-CT.

They’re often used if you have cancer to see if it has spread, or if you have suspected dementia or another cognitive impairment. Sometimes early risk of dementia shows up more clearly on a PET scan than other scans, though it isn’t widely used in the NHS at the moment.

PET scans of your coronary arteries are also sometimes used to help plan procedures, including heart bypass surgery.

2. What will a PET scan tell my doctor?

A PET scan detects the radiation given off by a radioactive material (called a tracer) injected into your arm. The radioactive material is attached to a type of sugar. The body treats this sugar as fuel and this allows us to see how much energy is being used by, for example, different parts of the brain.

A PET scan detects the radiation given off by a radioactive material (called a tracer) injected into your arm.

In the heart, it can be used to assess whether areas of the heart have died following a heart attack so are no longer using sugar, or whether there are areas of inflammation or infection which use more sugar.

Rapidly dividing cancer cells also use lots of glucose, which is why the test is useful for showing the spread of cancer.

Other PET scans can study blood flow through the heart as evidence of narrowings or blockages in the arteries, similar to SPECT scans.

3. What does having a PET scan involve?

You have an injection of radioactive material, then you’ll go into a ring-shaped scanner.

Image of a PET scanner

4. Do I need to do anything to prepare for my PET scan?

Your appointment letter will tell you if you need to do anything. Sometimes you may be asked not to eat anything during the few hours before the scan.

5. How long will my PET scan last?

You’ll be there for up to several hours. After the injection of radioactive dye, you lie down while the dye travels to the part of you that the doctors want to examine (for example, the fatty plaque in your arteries).

The scan is similar to a normal CT or MRI scan. It takes about 30 minutes. Afterwards, you’ll probably have to stay for a couple of hours while the radioactivity wears off.

6. Will having a PET scan be painful?

You may feel a prick from the injection, that’s all.

7. Are there any risks with PET scans?

You’ll receive an extremely low dose of radiation that shouldn’t pose a risk to your health. The benefit to you will outweigh any possible risk.

You might have to wait before going home after a PET scan. We try to keep radiation exposure low, and we don’t want the general public to be exposed to someone who might be slightly radioactive.

If it’s a PET-CT, there will be an additional radiation dose from the scanner, but this will still be a small amount.

8. Is there anyone who shouldn’t have one?

Pregnant women shouldn’t have a PET scan. If you are breastfeeding, ask your doctor for advice. People with non-MRI-compatible implants, including some pacemakers, would not be allowed to have a PET-MRI scan either.

PET scans of the heart

PET scans of the heart

9. What are the latest PET scan developments?

New radioactive dyes are being developed all the time, which are getting better at highlighting specific disease processes (especially cognitive decline and dementia).

In 10 years, it is quite possible there will be specific agents to pick up specific processes.

Another improvement is speed: a scan that once would have taken an hour can now take just 20 minutes.

There are also new uses for PET scans. For example, if you have atheroma (fatty plaque) in your arteries, then the PET scan can pick up whether it is active or not – a factor that affects your risk of having a stroke, heart attack or a burst blood vessel.

This isn’t yet routine for NHS practice but could become so in a few years’ time. With the support of BHF funding, we’re also developing more sophisticated ways to show blood flow in the brain. This is mainly being used for research but could become part of normal patient care. 

Professor Joanna WardlawProfessor Joanna Wardlaw

  • Professor of Applied Neuroimaging, Head of Division of Neuroimaging Sciences and Director of the Brain Research Imaging Centre, University of Edinburgh
  • Honorary Consultant Neuroradiologist at NHS Lothian
  • Author of more than 400 publications
  • Recipient of University of Edinburgh Chancellor’s award for research and the British Society of Neuroradiologists President’s medal
  • Her groundbreaking studies have changed how patients with stroke are treated all over the world

Discover Professor Wardlaw's research into lacunar stroke and dementia.

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